1. Service Provider Networks (SPNs)
It is increasingly common for people to use client-side devices to communicate with other devices via cellular wireless communication systems operated by wireless-service providers (i.e., service provider networks (SPNs)), whether those devices are directly connected to the same SPN or to another system (such as another SPN or a transport network, as examples) to which that SPN directly or indirectly provides access. These client-side devices are generally referred to in this disclosure as mobile devices, though this term is intended to broadly encompass various devices known by terms such as mobile stations, access terminals, user equipment, cellphones, smartphones, wireless-communication devices, personal digital assistants (PDAs), tablets, laptops, air cards, Universal Serial Bus (USB) devices, and/or any other device(s) capable of functioning as a mobile device according to this disclosure. Via the SPN, mobile devices generally engage in communications such as voice calls, packet-data sessions, text messaging (e.g., Short Message Service (SMS) messaging), and the like.
Furthermore, the wireless communication between the SPN and a given mobile device is typically bidirectional in nature. The component of that communication that is sent from the SPN to the mobile device is described as being sent on what is known as the forward link, while the component that is sent from the mobile device to the SPN is described as being sent on what is known as the reverse link. On both links, the wireless communications are typically formatted in accordance with a wireless-communication protocol, one example type of which is code division multiple access (CDMA), where CDMA networks that operate according to industry specifications (IS) such as IS 95 and IS 2000 are often referred to as 1×RTT (or “1×”) networks, where 1×RTT stands for Single Carrier Radio Transmission Technology.
Some SPNs operate in accordance with a particular type of CDMA protocol known as Evolution Data Optimized (EV DO). These SPNs are generally configured to operate according to one or more versions of IS 856, and are designed to provide high-rate packet-data service to access terminals using a technique on the forward link known as time-division multiplexing (TDM) and using what is essentially 1× technology on the reverse link. More generally, SPNs can be arranged to operate according to any of numerous other protocols, some examples of which are Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS), WiMAX (IEEE 802.16), time division multiple access (TDMA), Global System for Mobile Communications (GSM), Wi Fi (IEEE 802.11), and the like. And certainly some SPNs are arranged to provide service in accordance with multiple protocols.
In typical SPNs, the entities with which mobile devices communicate over the air interface are known by terms such as base station and access node, terms that are used at different times in different ways to refer to different entities. For example, the term base station is sometimes used to refer simply to a device also known as a base transceiver station (BTS), which contains the hardware, antennas, and other components that cooperate to actually conduct the over-the-air communication with the mobile devices on behalf of the SPN. In LTE networks, a BTS is typically referred to as an eNodeB, which stands for Evolved Node B, named as being an evolved version of a Node B in a UMTS Terrestrial RAN (UTRAN). At times, however, the term base station or access node is used to refer in combination to (i) one or more BTSs and (ii) a device known as a base station controller (BSC) (or radio network controller (RNC)), which controls the BTS(s) and connects it (them) to the rest of the network and beyond.
The base stations for these networks are typically not associated with any subscriber or small group of subscribers in particular; rather, they are placed in publicly-accessible locations and are used by the provider's customers generally. These base stations collectively blanket large geographic areas with coverage; as such, they are referred to generally and herein as “macro-network base stations” or “macro base stations” and the network they collectively form, or to which they collectively belong, is referred to generally and herein as the “macro network.”
Mobile devices and macro base stations conduct communication sessions (e.g. voice calls and data sessions) over what are known as carrier frequencies. Furthermore, macro base stations may provide service in a given coverage area on one carrier frequency, or on more than one carrier frequency. Mobile devices in the coverage area are configured to wirelessly communicate with the macro base station—and thus with the SPN—by tuning to at least one of the carrier frequencies on which the SPN provides service in the coverage area.
Procedures for initiating and managing wireless communication between macro base stations and mobile devices vary depending on the network architecture employed. Generally, coverage areas in the SPN emit pilot or reference signals to enable mobile devices to connect to such coverage areas. Mobile devices in the SPN regularly scan for such signals to identify coverage areas with which to connect, or to which to hand off. Thus, a mobile device may measure signal strengths of detected pilot signals and send a message that includes an indication of the measured signal strengths. The message may be received by a base station, and the SPN may then determine how to manage communication with the mobile device, such as whether to initiate a communication link, whether to instruct the mobile device and base stations to hand off an ongoing call, and so on. Such management determinations can be made by a centralized controller, such as an RNC in a CDMA system, or by distributed network controllers co-located with the base stations, such in an LTE system.
2. Femtocells
To address gaps in macro-network coverage (e.g., in buildings) and for other reasons, macro-network service providers may also offer devices referred to herein as femtocells. A typical femtocell may be approximately the size of a desktop phone or Wi-Fi access point, and is functionally a low-power, low-capacity version of a macro base station. A typical femtocell uses a normal power outlet, perhaps with a transformer providing a DC power supply. The femtocell may have a wired (e.g., Ethernet) or wireless (e.g. Wi-Fi) connection with the user's router, and would thus have connectivity to the Internet and/or one or more other packet-data networks. A femtocell may establish a virtual-private-network (VPN) connection over the Internet with an entity (e.g., a VPN terminator) on the macro-network provider's core network. The femtocell can then securely communicate with the VPN terminator and thereby communicate with other entities of the macro network.
A typical femtocell also has a wireless-communication interface configured to wirelessly communicate with mobile devices according to wireless protocols such as CDMA, LTE, and the like. The femtocell may act as a micro base station to provide local wireless coverage on the macro-network provider's network via the user's Internet connection. Typically, a femtocell will provide service on a single carrier frequency (or on a single carrier frequency per technology, where multiple technologies, such as CDMA and EV-DO, are supported). The femtocell will typically also transmit a pilot beacon, which includes administrative messages and parameters that mobile devices can use to connect with the femtocell. The pilot beacon may include information to facilitate a handoff of a mobile device from a macro base station to the femtocell. To inform mobile devices of the femtocell, the pilot beacon may be transmitted on one or more of the macro-network carrier frequencies on which the SPN provides service in that area.